1. Field of the Invention
The present invention relates to a ceramic-steel joined body suitable for engine parts such as a tappet, a valve lifter, a rocker arm, a cam shaft, a turbo-charger rotor, and the like, and other various industrial constituent parts; and further relates to a method of producing such a joined body.
2. Related Art
Year by year, the abrasion resistance properties required for engine parts have become more severe with developments in higher-output operation and higher-speed rotation of engines. Although attention has been given to ceramics as a material capable of responding to the more severe requirements, ceramics are so expensive that it is not practical to form whole parts from the material because the cost of the product would become too great. However, severe abrasion resistance is required only for a specific portion of the parts, and it is not necessary to form whole engine parts from ceramics. In view of this, a technique of brazing a ceramic chip to a certain portion of a metal part is disclosed in Japanese Patent Unexamined Publication No. Hei-2-55809, which is commonly owned with the subject application. In this conventional technique, a metal part except for the ceramics is hardened to HRC45 or more.
There is a defect in this conventional technique in that if an entire metal part is hardened to HRC45 or more, the part is likely to break when subjected to a strong impact load.
On the other hand, if only the portion of the part where high impact strength is required is subjected to annealing in order to obtain toughness after the entire metal part has been hardened by brazing heat-treatment, problems of reduction in quality occur such as oxidation of the brazing portion or the like because the annealing temperature is high (e.g., hundreds of degrees Centigrade).
Further, in the case where quenching is performed after brazing is performed on the steel (the whole of which may have a hardness of about HRC30 through brazing heat-treatment), problems are caused by strength reduction in the brazing portion because of heat at the quenching and the increase in the number of steps after the brazing.